The goal of the research proposed in this renewal application is to improve dental amalgam by applying knowledge of amalgamation kinetics. By changing amalgamation kinetics, the microstructure and therefore the properties of dental amalgam can be modified. Three components of amalgamation kinetics (dissolution, nucleation and growth, and solid state diffusion) will be studied separately and as integral parts of the total amalgamation reaction. Understanding of amalgamation of Ag-Sn-Cu alloys, where the Cu concentration is greater than 8 wt.%, will be emphasized. These high copper amalgams have better creep resistance, compressive strength, and resistance to marginal breakdown than conventional amalgams. The present investigators have observed Cu6Sn5 crystals dispersed in the gamma 1 (Ag2Hg3) matrix of these amalgams and have suggested that these crystals may contribute to the improved properties of these amalgams. Therefore, focus of the amalgamation kinetics research will be on altering the size, distribution and quantity of Cu6Sn5 crystals in order to optimize their effect on amalgam properties. To better understand the role of dispersed Cu6Sn5 crystals in improving the properties of high copper amalgams, creep and compressive tests of high copper amalgams will be conducted. Samples fractured in compressive tests and samples used in creep tests will be examined with a SEM. The effect of changes in microstructure on creep resistance and compressive strength will be sought. To determine the effect of the Cu6Sn5 crystals on marginal breakdown, a "chewing" machine will simulate mastication forces on Class II restorations placed in acrylic molars. Tests will be run in air and in corrosive environments to separate breakdown due to corrosion from breakdown due to mechanical deformation. Fractured margins of these amalgams will be examined with a SEM to determine the cause of marginal failure. The data on creep resistance, compressive strength, and marginal breakdown of high copper amalgams should suggest microstructures which will optimize these properties. Knowledge of amalgamation kinetics will be used to produce these microstructures in amalgams made from high copper and Ag-Sn + (x) alloys.